It is known in the art relating to exhaust driven engine turbochargers to provide a rotor including a turbine wheel and a compressor wheel connected by a shaft for rotation together about an axis. In some cases, the shaft is formed as an extension of the turbine wheel. Separate shaft and wheel components may be welded together before final machining. Alternatively, a steel shaft may be connected to the turbine and to the compressor wheel by separate connecting means. Commonly, the impeller or compressor wheel is made of aluminum alloy to minimize the rotating mass.
Various types of connecting means have been provided for aligning and connecting the wheels and the shaft for axial rotation. Where the connecting means extend through the compressor wheel and clamp the wheel in compression against the shaft, the design should avoid excessive variations in clamping load due to differential thermal growth and the effects of centrifugal force on the steel and aluminum during varying operating and stationary conditions.
The means for connecting the compressor impeller wheel and the turbine wheel to the shaft are also important because the rotor must be disassembled after balancing in order to assemble the rotor into the turbocharger. Upon reassembly of the rotor, the repeat balance must preserve the original balance as far as possible without actually rebalancing the rotor in the turbocharger assembly. A design of turbocharger rotor which meets these requirements is disclosed in U.S. Pat. No. 6,364,634, issued Apr. 2, 2002 to the assignee of the present invention.